With the PNG 8-bit color format, you can have image transparencies that:
- Are greater than one color. (GIF provides transparency in one color only.)
- Can be achieved while maintaining a small file size. You can also use PNG-24, but the file size is larger.
These files have a 256 color depth (reducing the file size) and support 8-color transparency (preventing image halos as seen with GIF transparencies).
For more information, see http://microsite.omniture.com/t2/help/en_US/s7/is_ir_api/index.html#is_api-http_ref-fmt.